IN THE NAME OF ALLAH, THE MOST GRACIOUS, THE MOST MERCIFUL
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Presentation Of
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Computer Network
A computer network consist of two or more computers that are
connected together to share information and resources.
The resources may include printers, hard disks, scanners or programs etc.
Applications and Benefits of Computer Networks
Computer networks are very useful to share data. Information and resources
Among different users.
Some important benefits of computer networks are as follow:
1.
2.
3.
4.
5.
Information and resource sharing
Money saving
Communication
Internet access sharing
Entertainment
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Disadvantages of computer network
Some disadvantages of computer networks are as follows:
1.
2.
3.
4.
Hardware, Software and setup costs
Hardware and software management cost
Data security concerns
Undesirable sharing
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Hardware, Software and setup cost
Setting up a network required an investment in hardware software planning
Designing and implementing the network,
Data Security Concerns
A poorly-Secure network puts critical data at risk. the hacker may access
The network and get important data or may damage the data.
Hardware and software Management Cost
Managing a network is a complicated task. The proper maintenance of a
Network requires time and expertise.
Undesirable Sharing
Networking allows the sharing of undesirable data, voices easily spread
Over networks and internet.
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Types of Computer Networks
Computer Networks are categorized according to:
1. How they are organized physically
2. The way they are used
3. The distance over which they operate
Three main types of Computer Network are:
1. LAN – Local-Area Network
2. WAN – Wild-area Network
3. MAN – Metro-Politan Area Network
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LAN – Local-Area Network
LAN Stands for local area network. It is the most common type of network
It covers a small area. It usually connects the computers and other devices
Within one office or a building or group of buildings. LAN is often used to share
Resources such as hard disk and programs
Benefits / Advantages of LAN
Some important advantages of LAN are as follows:
1. Resource Sharing
The resources like printers, CD Room Drivers, Hard Disk and software
Can be share using LAN.
2. Communication
The user in LAN can easily communicate with each other. They can
Also transfer data easily and rapidly between different computers in the network
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3. Data Security and Management
LAN can manage important data in a better way data can be
Centralized on shared servers instead of storing it on different computers
4. Internet access Sharing
LAN allows multiple users to share a single internet connection an
Organization can purchase one high speed connection and share it on different
Work station in LAN
Disadvantages of LAN
Some important disadvantages of LAN are as follows:
1. Privacy Threat
LAN can be threat to users privacy. The network administrator can access
Personal files of users
2. Expensive to install
LAN generally saves money over time. How ever, it may require high initial
Cost of installation. The cables, network card and software are expensive
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WAN – Wild-area Network
WAN stands for wild area network. This type of network covers a large area. It
Connects computers and other devices in different cities and countries. WAN
Usually consists of several LANs connected together computers in a WAN are often
Connected through telephone lines, they can also be connected through lease
Lines or satellites
Examples:1. The network connecting the ATM of a bank located in different cities.
2. The network connecting NADRA offices in different cities of Pakistan.
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Advantages of WAN:Some important advantages of WAN are as follows:
1. Communication Facility
1. A big company may exist at multiple locations in a country. The
Employees can communicate using WAN it saves long distance
Phone calls. Video conferencing is another use of WAN where users
Can communicate with each other through their computer system.
2. Remote Data Entry
Remote data entry is possible in WAN. The user can sit at any
location
And enters updates and process data on any computer attached to WAN.
3. Entertainment
WAN can facilitate many types of games and entertainment to
the User.
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Disadvantages of WAN
Some important disadvantages of WAN are as follows:
1. Hardware, Software and setup costs:
Setting up a WAN requires an investment in hardware software
Planning designing and implementing. The cost of devices used in WAN are very
Expensive.
2. Hardware and Software Management Costs:
Managing a WAN is complicated it requires intensive training
A network manager usually needs to be employed.
3. Data Security Concerns.
A poorly secure WAN puts critical data at risk. It may expose
Data to hackers, unauthorized access and even sabotage. Virus can spread
Quickly across the WAN if it enters the central backing store.
4. Failure of server:
If a server fails all computers connected with a server or effected.
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MAN – Metro-Politan Area Network
MAN stands for Metro-Politan area Network. This type of network
covers an area Of a city. MAN is large than LAN but smaller then
WAN. It is usually used to Connect two or more LANs in a city or town
Advantages of MAN
1. MAN covers a larger area then LAN
2. It provides higher data speed than LAN
Disadvantages of MAN
1. It is more expensive than LAN
2. It is difficult to maintain as compared to LAN
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Difference between WAN and LAN
Sr.
LAN
WAN
1
LAN is used to connect computers
at one place
WAN is used to connect computers
Anywhere in the world
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LAN covers limited area
WAN can cover more distance area
3
Data transfer is very fast in LAN
i.e. from 10 to 1000Mbps
Data transfer speed is slow in WAN
i.e. from 56Kbps to 50MBps
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LAN less costly
WAN is expensive
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LAN is usually connected through
wires
WAN is usually connected through
Telephone lines
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Data Communication:
Data communication is a process of transferring data electronically from one
Place another. Data can be transferred by using different media.
Basic elements of Data communication
1.
2.
3.
4.
Sending devices
Receiving Devices
Communication Devices
Transmission Medium
Sending Device:
A device that sends the data is called sending device. It is also called
sending device or transmitter. The Sending device can be a computer, fax machine or
mobile phones etc
Receiving Device:
A device that receives the message is called receiving device. A
receiving device can be a computer, fax machine or mobile phone etc.
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Communication Devices:
Communication devices are used to transmit messages b\w
sending and receiving device through communication medium. The sending and receiving
devices must contain communication devices for communication.
Transmission Medium:
Transmission medium is used to carry messages from one place to
another. It is also called communication channel.
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• Types of data transmission:
The two types of data transmission are as follows:
1) Digital data transmission
2) Analog data transmission
1) Digital data transmission:
The transfer of data in the form of digital signal is called digital
data transmission. Digital signal is a sequence of voltage represented in
binary form. The digital signals are in the form of electrical pulses of ON or OFF.
2) Analog data transmission:
Analog data transmission is the transmission of data in a
continuous wave form.
For Example, Sound waves are analog signals. When we talk, we emit sound
waves that consist of wave forms of high or low pressure. Analog signal is
measured in volts and it’s frequency is in Hertz (Hz).
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Network Topologies
A Network can be configured or arranged in different ways.
The Physical Layout or arrangement in different ways.
The physical layout or arrangement of connected devices in
A network is topology. Different network topologies are as follows:
1) Bus Topology
2) Ring Topology
3) Star Topology
4) Tree Topology
5) Mesh Topology
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Bus Topology:
Bus topology is the simplest type of network. It supports a small number of
computers. In bus topology, all computers or network nodes are connected to a common
communication medium. This medium is often a central wire known as bus. The terminators
(Device attached to the end points of a bus network and purpose is to absorb signals so that
they may not reflect back down the line.
Working:
Sending computer sends the data and destination address through the bus
the data and address move from one computer to the other in the network. Each computer
checks the address if it matches keeps the data otherwise moves to the next computer.
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Advantages:
1) Simple and easy
2) Requires small length of cable
3) Less expensive
Disadvantages:
1) Difficult to troubleshoot
2)Supports small number of computers
3) If number of computer increase, network speed will slow.
Star Topology:
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All computers in this network are connected to a hub. Star topology
is the best LAN Topology
Working:
Sending computer sends the data to hub. Hub sends the data to the
receiving computer. Each computer in this topology communicates to
central hub.
Advantages:
1) Easy to maintain and modify network.
2) Adding or removing computers can be done without disturbing the network.
3) Finding faults is easy.
Disadvantages:
1) If central hub fails the whole network breaks down.
2) Requires large length of cable to connect computers.
3) More expensive.
Ring Topology:
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In this topology, each computer is connected to the next computer with
the last one connected to the first. Thus, a ring of computers is formed.
Working:
Every computer is connected to the next computer in a ring.
Each computer receives message from the previous computer and
transmits it to the next computer. The message flows in one direction.
The message is passed around the ring until it reaches the correct
destination computer.
Advantages:
1) It is less expensive than star topology.
2) Every computer has equal access to the network.
Disadvantages:
1) Failure of one can affect the whole network.
2) It is difficult to troubleshoot.
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Tree Topology:
A tree topology combines the characteristics of bus and star topologies.
It consists of different groups of computers attached in star topology.
The groups are then connected to a bus backbone cable.
Tree topology is used for the expansion of an existing network.
Advantages:
1) It provides point to point wiring for individual segments.
2) It is supported by several hardware and software vendors.
Disadvantages:
1) Overall length of each segment is limited by the type of cabling used.
2) If the backbone line breaks, the entire segment goes down.
3) It is more difficult to configure and wire than other topologies.
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Mesh Topology:
In a mesh topology, every device in the network is physically connected
to every other device in the network. A message can be sent on
different possible paths from source to destination. Mesh topology
provides improved performance and reliability. Mesh networks are not
used much in local area networks (LAN).
Advantages:
1) If one link becomes unusable, it does not harm the entire system.
2) It is easy to troubleshoot.
Disadvantages:
1) A full mesh network can be very expensive.
2) It is difficult to install and reconfigure.
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The path through which data is transmitted from one place to another is called
channel.
This is also known as Communication Media or Transmission Media
There are Two types of Communication Media
1. Bounded Media
2. Unbounded Media
1.Bounded Media
In bounded Media Communication Devices are connected with each other by
a physical Media like wires.
Some examples of Bounded media for communication are as fallows
1. Twisted Pair
2. Coaxial Cable 3. Fiber Optics
Twisted Pair Cable have two types:
1. Shielded Twisted Pair ( STP )
2. Unshielded Twisted Pair ( UTP )
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2.Unbounded Media
In Unbounded Media Communication Devices communicate with each other
Through air or space using broad cast radio signals, microwave signals and
Infrared signals.
Below are the examples of Unbounded Media:
1.
2.
3.
4.
5.
Microwave
Communication Satellite
Cellular Radio
Broadcast Radio
Infrared
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Communication and Network Devices
The hardware use to transmit data, instructions and information between a
Sending and receiving device is called communication device.
Different Types of Communication devices are as follows:
1.
2.
3.
4.
5.
6.
7.
Modem
Network Card
Wireless Access Point
HUB
Network Switch
Network Bridge
Router
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Modem
Modem stands for modulator it is commonly used communication
device Modem sends and receive data from one computer to another on
the Internet telephone line. The sending and receiving computers both Must
have modems
Types of Modem:
1.
2.
3.
4.
5.
6.
External Modem
Internal Modem
Wireless Modem
Cable Modem
DSL Modem
Satellite Modem
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External Modem
External Modem is attached to the system unit as an external device through
Telephone line. It is connected to the telephone wall jack by another cable
Internal Modem
Inter modem is a circuit board that is inserted into an expansion slot on the
Mother board. internal modem can not be moved form one computer
To another computer
Wireless Modem
A wireless transmit the data signals through the air instead of cable. It is also known
As radio frequency modem. It is designed to work with cellular technology and
Wireless local area network.
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DSL Modem
DSL Modem allows faster transmission over the standard telephone line
It is faster then IDSL.
There are two types of DSL Modem
1. ADSL Modem
2. SDSL Modem
ADSL Modem
It stands for asymmetric digital subscriber line. It uses faster
Transmission down stream than upstream. It is frequently used for faster
Inter services. It provides the upload speed of up to 640Kbps and download
Speed of up to 8.1Mbps.
SDSL Modem
It stands for symmetric digital subscriber modem. It uses the
Same transmission rate for both directions. It transfers data at 3Mbps
Approximately in both directions.
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Cable Modem
Cable Modem is also known as broadband modem. Cable modem is a
Stand alone device connected with a cable to USB port. It sends and
Receive data over the cable television network. It provides faster internet
Speed than dialup modem DSL modem and ISDN
Satellite Modem
It is used to send and receive data using satellite technology. It is
Commonly used for high speed internet service. Many satellite internet
Services use satellite technology for down stream data only
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Net Work Card
Network card is a communication device. It is also card called Network
interface card or LAN adapter. It is used to connect a Computer to a network. It is
circuit board installed on the mother Board. Now a days most computer systems have
a network card Built into the mother board. Each computer on the network must have
A network card
Wireless Access Point
A wireless access point is a central communication device. It allows
Computer and other devices to transfer data wirelessly among themselves Or to a
wired network. Wireless access point have high quality antennas for optimal
signals.
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HUB
A hub also called concentrator or multi station access unit (MAU). It provides a
central point for cable in a network. Hubs also transmit signals and have multiple ports to
which devices are connected.
Router
A router is a communication device that connects multiple computers or other
Routers together. It connects multiple networks using similar or different protocols.
It manages the best route between any two communication networks.
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Data Transmission Mode / Communication Direction
The way in which data is transmitted one place to another is called data
Data transmission mode or communication direction.
Types of Transmission Modes
There are three types of data transmission mode which are as follows:
1. Simplex Mode
2. Half duplex Mode Traffic
3. Full Duplex Mode
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Simplex Mode
In Simplex mode data can flow only in one direction. It can not be moved
In both directions. It operates in a manner similar to a one way street. The
Direction of flow never changes. A device with simplex mode can either
Send or receive data. It can not perform both actions.
Examples:An example is a traditional television broad cast the signal is send from the
Transmitter to TV antenna. There is no return signal.
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Half Duplex Traffic
In half duplex mode data can flow in both directions but not at the same time.
It is transmitted one way at one time. A device with half duplex mode can
Send or receive data but not at the same time. This is why the speed of half
Duplex mode is slow.
Example:
An example of half duplex is a narrow bridge that can carry single
Vehicle at a time. The traffic from side A stops while the vehicle from the side B
Cross the bridge.
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Full Duplex Mode
In full duplex mode, data can travel in both directions simultaneously. Full
Duplex is a faster way of data transmission as compared to half duplex.
Time is not wasted in changing the direction of data flow.
Example:
A telephone is a full duplex device, both persons can talk
At the same time. Another example of full duplex communication is a auto
Mobile traffic on a two lane road.
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Network Protocol:
A standard used by networks for communication between different
devices Connected to a network is called protocol. It represents an agreement
Between the communication devices. A protocol defines what is
Communication, how it is communicating and when it is communicated.
The device can not communicate with out a protocol.
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Protocol Functions
The main functions of protocols are as follows:
1. Data Sequencing
3. Data Flow
2. Data Routing
3. Error Control
Data Sequencing
A process of breaking a long message into smaller blocks is called data
Sequencing. A long message is divided into smaller packets of same size.
This technique reduces the amount of data that is retransmitted if an error is
Detected.
Data Routing
Data routing is a process of finding the most efficient path between source
And destination before sending data. This is technique increases the
Efficiency of data communication,
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Data Flow
All computers are not equally efficient in speed. Data flow is a process that
Controls data transmission properly if the sender computer is faster than the
Receiver computer
Error Control
Error detecting and recovering is an important function of communication
Protocol. It ensures that data is transmitted without errors. It also solves problem
If an error is detected.
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Key elements of Protocol
Three key elements of a protocol are as follows:
1. Syntax
2. Semantics
3. Timing
Syntax
Syntax refers to the structure or format of data. For example a protocol may
Expect the first eight bits of data as the address of the sender, the second eight
Bits as the address of the receiver and rest of the stream as the message itself.
Semantics
Semantics refers to the meaning of each section of bits. It includes how should a
Particular pattern be interpreted and what action should be taken. For example an address
may identify the router to be taken or the final destination of the message
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Timing
Timing indicates when data should be sent and how fast can not sent.
For example a sender may produce data at 100Mbps when the receiver
Can process data of at only 1Mbps. The transmission will over head the
Receiver and data will be lost.
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Types of Protocols
Some important protocols are as follows:
1. Ethernet
2. Token Ring
3. FDDI
4. ATM
5. TCP
6. UDP
7. FTP
8. SMTP
9. POP3
10. HTTP ( hypertext transfer protocol
11. HTTPS ( hypertext transfer protocol secure